GC-IRMS: Differentiating natural and synthetic sources of menthol by carbon and hydrogen isotope fingerprints

Product Manager

Sandra Forbes

Goal

Trace the origin of menthol using carbon and hydrogen isotopes.

Introduction

Menthol serves as a fundamental component in various widely utilized everyday products, including mouth fresheners, food items, chewing gums, fragrances, cosmetics, tobacco, and pharmaceuticals. It can be sourced naturally, such as from mint oil extracted via steam distillation of Mentha arvensis[1], or synthesized through diverse chemical pathways.

Natural products are frequently subjected to adulteration, such as being blended with more affordable synthetic counterparts, and the variability in menthol sources provides an avenue for economically driven fraudulent activities. The mint industry is experiencing steady growth, with an estimated total market value of around 1.2 billion US dollars[2]. Nevertheless, the price and availability of menthol are subject to fluctuations influenced by climatic conditions, which in turn affect the economies of the world's major mint oil producers, namely India (80%), China (9%), Brazil (7%), and the United States (4%)[1]. To safeguard both consumers and producers, a dependable method is necessary to prevent the mislabeling of products containing menthol.

Determining whether menthol originates from a natural or synthetic source can be achieved by examining the carbon and hydrogen isotope fingerprints.

This application brief presents the findings of carbon and hydrogen isotope analysis conducted on 10 menthol samples using Gas Chromatography Isotope Ratio Mass Spectrometry.

Carbon and hydrogen isotope fingerprints of menthol

Menthol possesses a distinctive chemical identifier, akin to a fingerprint, which enables its unique identification. The carbon isotope fingerprints (δ¹³C) exhibit variations across different plant groups, primarily due to the diverse photosynthetic mechanisms they employ and the environmental conditions they are subjected to[3]. The hydrogen isotope fingerprint, on the other hand, is intricately linked to local and regional rainfall patterns. Moreover, it can also be affected by agricultural cultivation methods, soil - related processes, and the geological attributes of the specific locale[4]. By integrating the carbon and hydrogen isotope fingerprints, it becomes feasible to evaluate the origin of menthol.

Results

In this investigation, ten menthol samples underwent analysis, with each sample being examined in triplicate. The carbon isotope fingerprints exhibited a range spanning from -26.8‰ to -31.2‰, with the standard deviation (STDEV) of individual measurements being less than 0.09‰ (n = 3). Meanwhile, the hydrogen isotope fingerprints varied from -70.1‰ to -377.9‰, with the STDEV of individual measurements staying below 1.6‰ (n = 3).

By integrating the carbon and hydrogen isotope data into a two - dimensional XY plot (as illustrated in Figure 1), a clear distinction was made between menthol obtained from natural sources and that produced synthetically. This approach offers a robust framework for identifying the sources of various sample types containing flavoring agents, which are extensively utilized in the food, pharmaceutical, and cosmetic industries.

Figure 1. Combined C and H isotope fingerprints of menthol samples.

Conclusions

Isotope fingerprints examined through GC - IRMS serve as a highly effective means to ascertain the origins of flavoring agents, such as menthol, thereby facilitating accurate product labeling. This is of paramount importance for fostering consumer trust, safeguarding brand reputation, and ensuring stable revenue for producers, while also playing a crucial role in curbing fraudulent practices.

Equipped with the GC IsoLink II IRMS System, laboratories acquire an efficient analytical approach that hinges on the compound - specific identification of isotope fingerprints within intricate matrices. The reliability of this solution stems from its optimal GC resolution capabilities. Subsequently, it employs a fully automated and distinctive combustion/pyrolysis system to tackle complex analytical hurdles.

References

1. Report on Mentha Oil, Word Press, published 31st October 2013.

2.http://www.perfumerflavorist.com/flavor/application/mint/Taking-a-Fresh-Look-atMint-441531643.html.

3. O’Leary, M.H., (1988), BioScience 38, 328.

4. Dansgaard, W., (1964), Tellus. 16, 436–468.

Aladdinsci: https://www.aladdinsci.com